SPOILER ALERT: This blog is for those who are watching season four of Mad Men on BBC4. Don't read on if you haven't seen episode seven – and if you've seen more of the series, please be aware that many UK viewers will not have done so…

"It's not my fault you don't have a family or friends or any place to go." Peggy

Since this episode aired in the US, people have been raving about it being Mad Men's finest. It was a lot to live up to, but The Suitcase – written solely by Matthew Weiner – is a masterpiece. Like The Sopranos' Pine Barrens, it's focused almost completely on two characters sharing a dark night of the soul. With Peggy and Don as Paulie and Christopher and Duck as the Russian mobster.

The Suitcase is set against the backdrop of the second Ali-Liston fight, as SCDP's creative team are struggling to come up with a decent idea for Samsonite. The key narrative hook is the message that Miss Blankenship takes from California for Don which hangs over the sombre 45 minutes. Both the audience and Don know the nature of the call and, in order to avoid it, Don embarks on a self-destructive binge of drink and work that leaves Peggy as collateral damage.

Rather than go to a birthday dinner with her wet boyfriend Mark, Don tells Peggy to stay and work on Samsonite. This almost immediately leads to a huge argument about who got the credit for Glo-Coat, with Don once again wondering why money doesn't equate to contentment for his junior female staff. Peggy's bathroom tears provided a nice nod to a scene in the second-ever episode in which Peggy goes to the ladies' room and sees a woman crying, but this time it is her who bursts into tears in front of the mirror. They eventually make up, eat dinner in a roach-infested diner while listening to the fight, and then head back to the office where Don is violently sick from the gallons of whisky he's consumed.

She may have been furious but Peggy doesn't really want to leave. She has plenty of chances, making it to the elevator doors more than once before returning to Don. Initially this is out of duty – she admits she can't see anything of importance beyond SCDP's walls. But nor can she leave him to suffer by himself. When they tell each other about their dead parents and their feelings, we see their relationship once again as something deeper than just colleagues. It's clear Peggy needs a father (which is why she won't abandon him) and Don needs a mother. He had one in Anna but, as we saw her ghost pass through Don's office and into the good night, the baton has passed to Peggy. And he knows it. This whole sequence was incredibly moving. I unconsciously stopped writing notes as soon as Don made the call to Stephanie. We've seen his human side before, but this was a first for Peggy – who sees weakness in Don previously only hinted at.

Alongside all this is Duck. Last time we saw him he was being chucked out of the Clios. He's in no better state here, trying to win "Pee Wee" over with business cards for a fictitious agency before drunkenly finding her at the office. I've referred a couple of times to this comment by Horatio93 about Duck being a ghost of Don's future, and here the ghost catches up with itself as Duck comes in to win Peggy back from Don before calling her a whore. Which is enough to make Don channel Sonny Liston and wretchedly swing for him.

When the night is over, Don delves into his pressed-shirt drawer and looks immaculate once more. As he shows Peggy his Ali-inspired Samsonite idea, they share the briefest moment of physical contact which is Don's own, fragile way of finally saying thank you. Anna might have been the only person who knew him, but Peggy now feels like she does too. As if to make the point clear, Don asks her to leave his door open as she leaves. Previously, it – like he – would be closed.

Notes

• "You're such a Jew." What was Harry thinking? Good on Danny for pointing out his wretched hypocrisy.

• Peggy's roommate – "Rasputin" – is definitely not still Karen.

• Did anyone spot Don almost gagging at Miss Blankenship's coffee?

• A heavily pregnant Trudy bumps into Peggy in the loos. Has anyone caught Alison Brie in the very good Community?

• Roger's night out with the AA boys was enough to drive anyone to booze: "Did you know Freddy Rumsen collects Indian arrowheads?"

Lyle Evans Watch

• So Lyle Evans wasn't a Huckster. It was the doctor who removed Bert Cooper's balls. This almighty extract from Sterling's Gold explains:

"Bert Cooper hated me and I thought it was because he thought I'd be an ally of my father. But it turned out it was something to do with my joie de vivre, my romantic prowess (see tape three) including some time with the queen of perversions ... his secretary Ida Blankenship (you know what, don't use her name). But it was all about him hating my very youth all because the poor guy had been cut down at the height of his sexual prime by an unnecceasary orchiectomy ... Lyle Evans MD. I think he had him killed."

Culture Watch

• We're played out to Simon and Garfunkel's Bleecker Steet, from Wednesday Morning, 3am. The Ali fight took place on a Tuesday night, meaning that Peggy and Don's bonding happens – when else? – on a Wednesday morning at 3am.

20th Century Tales

• The team are all going to Loew's Capital Theatre to watch a feed of the second Ali-Liston fight up in Lewiston, Maine as Ali defended his WBC heavyweight title. David Remnick's glorious King Of The World tells the story of this bout in vivid detail. But, for most, its defining image is Neil Leifer's iconic photo which, indeed, makes it into the episode and Don's Samsonite idea.

• More sport came with the creative team's idea of using fresh-faced AFL signing Joe Namath in a Samsonsite ad. A prodigious college player "Broadway" Joe became one of the NFL's all-time greats but Don misjudges the zeitgeist - "He hasn't even played in a professional game yet."

• Duck "killed 17 men in Okinawa" and it felt like a surprise to see him overpower Don so easily.